1. Field of the Invention
The present invention relates to a fluid-filled vibration damping device utilizing vibration damping effects based on the flow behavior of a fluid sealed therein.
2. Description of the Related Art
Conventionally, there has been known a fluid filled vibration damping device utilizing vibration damping effects based on the flow behavior of a fluid sealed therein as a kind of vibration damping coupling body or vibration damping supporting body interposed between the members constituting a vibration transmission system. This vibration damping device has a structure where a first mounting member and a second mounting member are elastically connected by a main rubber elastic body, and a pressure-receiving chamber with part of its wall made of the main rubber elastic body and an equilibrium chamber with part of its wall made of a flexible film are formed, both chambers containing a non-compressible fluid sealed therein, and an orifice passage is formed through which the pressure-receiving chamber and the equilibrium chamber communicate with each other. The fluid-filled vibration damping devices with the structure described above include the one disclosed in U.S. Pat. No. 8,556,239, for example, and their application to engine mounts, body mounts, suspension member mounts and differential mounts of motor vehicles, and even to suspension bushes has been under consideration.
By the way, in case of applying a fluid-filled vibration damping device to an engine mount and the like, vibration damping effect is required against vibration in each of multiple frequency bands. Therefore, U.S. Pat. No. 8,556,239 presents a obstructing rubber elastic plate for the purpose of obtaining effective vibration damping effect against vibration with a higher frequency than the tuning frequency of the orifice passage. Then, against high-frequency, small-amplitude vibration, vibration damping effect obtained by low dynamic spring behavior is exerted by means of releasing the pressure in the pressure-receiving chamber into the equilibrium chamber triggered by a slight deformation of the obstructing rubber elastic plate.
However, as a result of further studies conducted by the inventor of the present invention regarding the fluid-filled vibration damping device described in U.S. Pat. No. 8,556,239, it was made known that there is some room for further improvement. In other words, in the structure of U.S. Pat. No. 8,556,239, the liquid pressure absorption effect is exerted due to a slight deformation of the obstructing rubber elastic plate in the thickness direction based on relative pressure fluctuation between the pressure-receiving chamber and the equilibrium chamber under a condition where the communication aperture that connects the pressure-receiving chamber and the equilibrium chamber with each other is shut off by the obstructing rubber elastic plate. In such structure as described above, vibration damping effect due to the orifice passage can be obtained effectively, while the wall spring rigidity of the pressure-receiving chamber is made higher based on the elasticity of the obstructing rubber elastic plate than when the pressure-receiving chamber and the equilibrium chamber communicate with each other, which poses a risk of not being able to cope with higher requirements for vibration isolation effect by low dynamic spring behavior.